1. Field of the Invention
The present invention relates to road information sensing system, method and program.
2. Description of Related Art
A previously known navigation system senses a current position of a vehicle and displays a map around the current position of the vehicle on a display device by retrieving it from map data. Furthermore, the navigation system indicates an own vehicle position mark, which indicates the current position of the vehicle, on the map. In this way, an occupant of the vehicle can recognize the current position of the vehicle. In general, such a navigation system senses the current position of the vehicle based on both of absolute position data, which is obtained through a satellite navigation using a GPS sensor, and relative position data, which is obtained through a dead-reckoning navigation using, for example, a gyro sensor and a vehicle speed sensor. In such a case, when the own vehicle position mark is displayed on the map through direct use of the sensed current position, the own vehicle position mark may possibly be deviated from a corresponding road on the map due to influences of, for example, an error between the road, which is indicated by the map data, and the actual road. Thus, a map-matching process is performed to coincide the sensed current position of the vehicle with the road on the map, so that the position of the vehicle based on the map indicated by the map data is obtained.
Various types of processes have been proposed as the above ma-matching process to improve a degree of accuracy of the own vehicle position on the basis of the map, which is indicated by the map data. For example, Japanese Unexamined Patent Publication No. H09-304093 recites one technique. According to this technique, there is set a parameter, which serves as a threshold value for determining whether the current position of the vehicle needs to be corrected to place the current position of the vehicle on the road on the map. Then, the map-matching operation may be performed through use of the parameter, so that the best map-matching operation may be performed even when a road density changes. Furthermore, Japanese Unexamined Patent publication No. 2005-207821 recites another technique. According to this technique, two dimensional road surface data, which includes a road width of each link that indicates a corresponding predetermined road interval, is formed. When the current position of the vehicle is not present in the road surface data, correction of the current position of the vehicle on the road on the map is performed, so that an error is reduced in comparison to a case where the map-matching is performed on the basis of the link (one dimensional line data).
As described above, in the navigation system, it is important to display the current position of the vehicle in a manner that coincides with the map. Even in a case where the map, which is indicated by the map data, differs significantly from the actual road, it has been demanded that the position of the vehicle is displayed in the manner that coincides with the road on the map.
In the recent years, it has been considered to implement an appropriate vehicle control operation, which is appropriate for a current state of a road, by linking the navigation system with the vehicle control operation. For example, in some cases, optical axes of left and right headlights, which are arranged in a vehicle front side, are made to be adjustable in a plane that is parallel with a road surface. Here, the optical axes of the left and right headlights are adjusted in accordance with the road state (a road direction on the vehicle front side), which is determined based on the map that is indicated by map data.
However, as discussed above, the previously proposed map-matching process is aimed to improve the degree of accuracy of the position of the vehicle on the basis of the map that is indicated by the map data, and an accuracy of the position of the vehicle on the basis of the actual road is not really considered. Thus, in a case where the degree of accuracy of the current position of the vehicle on the basis of the actual road is not sufficient, when the above technique is used in a vehicle control operation, timing for performing the vehicle control operation may possibly be deviated from appropriate timing due to, particularly, an error (an error in a front to back direction of the vehicle) of the current position of the vehicle along the road. This kind of the problem becomes particularly serious when the vehicle control operation is related to vehicle safety.